2. What is gravity? Galileo and Newton gave the name
gravity to the force that exists
between the Earth and objects.
Newton showed that the same force exists between all objects.
Even today, no one knows exactly
why objects attract each other.

3. An imaginary line from the sun sweeps out equal areas
The paths of the planets are ellipses with the center
of the sun at one focus.
An imaginary line from the sun sweeps out equal areas
in equal time intervals. Thus, planets move fastest
when closest to the sun, slowest when farthest away.
The ratio of the squares of the periods of any two
planets revolving about the sun is equal to the ratio
of the cubes of their average distances from the sun.

4. In 1666, Isaac Newton determined that the
same force that kept the planets in motion
must also exist between every object.
He stated that every object in the universe attracts
every other object in the universe. The force of attraction between two objects is directly proportional
to the product of their masses, and inversely proportional to the square of their separation distance.

5. F G m1 m2 = d2 In equation form:
F is the force of attraction, measured in NEWTONS,
between masses m1 and m2
G is the Universal Gravitation Constant, equal to
6.67 x N m2/kg2
m1 and m2 are the attracting masses, measured in
KILOGRAMS
d is the distance between their centers of mass,
and is measured in METERS

6. ( ) G Me v = r 1/2 v is in meters/sec
The Earth’s gravitational
attraction provides the
centripetal force needed to
keep a satellite in orbit.
The linear velocity v needed
to keep a satellite in a circular
orbit a distance r above the
Earth’s surface is given by: ( )
1/2 G Me v = r
v is in meters/sec
Me is the mass of the Earth in kilograms
r is in meters
G is the Universal Gravitation Constant

7. F g = m A gravitational field exists around every object
that has mass.
The gravitational field always points directly
toward the object’s center of mass.
The magnitude of the field is given by: F g = m
g is the field strength, measured in
Newtons/kilogram
m is the test mass, measured
in kilograms
F is the force of attraction, measured
in Newtons, on the test mass